The present invention relates to a semiconductor laser and, more particularly, to a laser device construction which ensures stable operation.
A semiconductor laser enjoys a limited period of life depending on deterioration at mirrors which function as the light emitting facet. Furthermore, a semiconductor laser may be damaged at mirrors if the semiconductor laser is driven in a considerably high optical power. The maximum optical power for catastrophic optical damage is about 10.sup.6 W/cm.sup.2 in the conventional semiconductor laser. Moreover, the photon density becomes high near the mirrors and, therefore, the beam absorption near the mirrors greatly influences the operating life period of the semiconductor laser.
It is a great desire to increase the maximum optical power for catastrophic optical damage to achieve a stable high power oscillation. Furthermore, the absorption of the high density laser beam near the mirrors must be restricted as low as possible in order to minimize the mirror deterioration.
To achieve the above desires, a window structure semiconductor laser has been proposed in, for example, Applied Physics Letters Vol. 34 (1979) P. 637, and a crank structure TJS laser has been proposed in, for example, Jpn. J. Appl. Phys. Vol. 21 (1982) Supplement 21-1, P. 347.
Generally, the conventional window structure semiconductor laser does not have the optical waveguide formed in the window region along the junction. Thus, the laser beam diffuses in the window region so as to reduce the beam amount directed to the stimulated region after the reflection at the mirror. This will reduce the oscillation efficiency, and will increase the threshold current.
Accordingly, an object of the present invention is to increase the oscillation efficiency in a window structure semiconductor laser.
Another object of the present invention is to provide a semiconductor laser which stably emits the laser beam in the visible spectral range.
Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
To achieve the above objects, pursuant to an embodiment of the present invention, an optical waveguide is formed also in the window region, whereby the beam waists for the field confined along and perpendicular to the junction exist at the mirror. More specifically, a V-shaped groove is formed in the substrate. A crescent active layer and a plane active layer are formed in the stimulated region and the window region, respectively, through a liquid phase epitaxy method under the same condition. This construction is named the window V-channeled substrate inner stripe (VSIS) laser.
The thus formed window region functions to suppress the higher transverse mode generated in the stimulated region so that only the fundamental transverse mode is transferred in the window region and developed through the mirror. The window VSIS laser of the present invention has low threshold current because the current is perfectly confined in the V channel by the inner stripe.
In a preferred form, an optical guide layer is formed on the active layer to ensure a stable operation at a high output power above 15 mW at one mirror, and to enable a pulse output over 100 mW at one mirror.